Feedback receiver for antenna tuner calculations

ABSTRACT

Some embodiments of the present disclosure relate to a feedback receiver comprising a threshold comparator configured to determine if the amplitude of a baseband signal is within a selection corridor (e.g., defined by an upper and lower threshold value). If the amplitude is within the selection corridor, a feedback receiver is configured to accumulate RF signal samples (e.g., amplitude and phase samples) over a time period. The accumulated RF signal samples, which correspond to substantially constant baseband amplitude values, are then averaged. The calculated averages are utilized for impedance measurements used tune an antenna tuner to limit impedance mismatch. By limiting RF amplitude and phase sample collection to associated baseband signals having an amplitude falling within the selection corridor, substantially equal average amplitudes and phases can be achieved over a relatively short measurement period (i.e., without the need for long measurement period).

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/273,563 filed on Oct. 14, 2011, entitled “Feedback Receiver forAntenna Tuner Calculations” in the name of Grigory Itkin and is herebyincorporated in its entirety.

BACKGROUND

Modern communication units (e.g., mobile phone hand sets) includeintegrated antennas configured to transmit and receive radio frequency(RF) signals. Integrated antennas are sensitive to external use cases(e.g., whether a hand is positioned on the phone, the position of a handon the phone, etc.) that alter the impedance of the integrated antenna,leading to an impedance mismatch between the antenna and RF circuitrywithin a transmitter. Such an impedance mismatch can degrade the powerradiated by a communication unit and increase the communication unit'ssensitivity to noise. From a user's perspective, impedance mismatchescan ultimately lead to a reduction in talk time or a dropped call. Toprovide better matching between RF circuitry in the transmitter and theantenna, handset designers use antenna tuners.

Conventionally, handset designers have arranged sensors inside thephone's package to detect the presence or absence of external use casesin an environment. Then the detected environment is compared with knownuse cases (e.g., “free space”, “hand on the phone”, “close to head”,“metal plate” . . . ) and a corresponding predetermined antenna tunersetting is chosen based on the detected use case. Unfortunately, thisconventional approach requires a large number of sensors inside themobile phone, which increases the phone's size and cost (particularly ifthere are a large number of possible use cases to be detected).Alternatively, a feedback receiver may be configured to determine animpedance of an output signal from a measured amplitude and phase of theoutput signal, and to adjust the antenna tuner settings based upon thedetermined impedance.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a transmitter having a feedback receiverthat is selectively operated based upon an amplitude of a basebandsignal to determine an impedance mismatch.

FIG. 2 is a block diagram of a transmitter that includes a polarmodulator in accordance with some embodiments.

FIG. 3 is a graph showing an exemplary baseband signal, illustrating acomparison of the amplitude of a baseband signal to one or morethreshold values.

FIG. 4 is a block diagram of a transmitter that includes an IQ modulatorin accordance with some embodiments.

FIG. 5 is a graph illustrating a plurality of impedances measuredaccording to a transmitter provided herein.

FIG. 6 is a flow diagram of an exemplary method for adjusting an antennatuning in accordance with some embodiments.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details.

The inventor has appreciated that for feedback receivers configured todetermine an impedance mismatch from a measured output signal amplitudeand phase, the feedback receiver has to average output signalmeasurements over a long period of time to reduce measurement errors. Ifconditions of the transmitter are substantially the same, the averagesshould provide a single impedance measurement value. However, widevariations in signal amplitude values (e.g., for signals with amplitudemodulation) along with other practical limitations (e.g., limits onmeasurement time and/or the size of memory used to store themeasurements) result in different averages that make for widespreadimpedance measurement values for the same conditions, and whichtherefore cause inaccuracies in the feedback receiver operation.

Accordingly, some embodiments of the present disclosure relate to afeedback receiver having a short measurement time and high accuracy forantenna tuner calculations. In particular, the feedback receiver isconfigured to selectively accumulate samples of an RF signal based uponan amplitude of a corresponding baseband signal, and to determine animpedance mismatch from the accumulated samples. In some embodiments,the feedback receiver comprises a threshold comparator configured todetermine if the amplitude of a baseband signal is within a selectioncorridor (e.g., defined by an upper and lower threshold value). If theamplitude is within the selection corridor, a feedback receiver isconfigured to accumulate RF signal samples (e.g., amplitude and phasesamples), provided by a two way directional coupler located between aradio frequency (RF) transmitter output and an antenna tuner, over atime period. The accumulated RF signal samples, which correspond toconstant or close to constant baseband amplitude values, are thenaveraged. The calculated averages are utilized for impedancemeasurements that are used to tune an antenna tuner to limit impedancemismatch. By limiting the collection of RF amplitude and phase samplesto associated baseband signals having an amplitude falling within theselection corridor, substantially equal average amplitudes and phasescan be achieved in a relatively short measurement period (i.e., withoutthe need for long measurement period). The substantially equal averagesprovide for substantially equal impedance measurement values that resultin high accuracy antenna tuner calculations.

FIG. 1 illustrates a block diagram of a transmitter 100 in accordancewith some embodiments. The transmitter 100 includes a baseband signalgenerator 102 configured to generate a baseband signal. The basebandsignal is provided to an RF transmission path 104. The RF transmissionpath 104 converts the baseband signal to an RF signal that issubsequently provided to an RF antenna 114 for transmission while thetransmitter is subject to a number of different use cases that may causeimpedance mismatch between the RF antenna 114 and the RF transmissionpath 104.

To limit impedance mismatch, the transmitter 100 comprises analysiscircuitry 106 that is operated to determine an impedance mismatchbetween the RF transmission path 104 and the RF antenna 114 based uponRF signal samples that are selectively collected based upon an amplitudeof the baseband signal. In one embodiment, the analysis circuitry 106includes a directional coupler 108 coupled between the RF transmissionpath 104 and an RF antenna tuner 112. The directional coupler 108 isconfigured to couple out a small part of the RF signal from thetransmission path 104 and to split this small part of the RF signal intotwo parts on paths 120. A measurement unit 118 is configured to measureforward propagating waves and reflected waves on paths 120.

The analysis circuitry 106 further includes a threshold comparator 124configured to receive an amplitude/magnitude of the baseband signal andto compare the received amplitude/magnitude to a selection corridordefined by upper and lower threshold values. In one embodiment, thethreshold comparator 124 is coupled between the baseband signalgenerator 102 and the RF transmission path 104. If theamplitude/magnitude of the baseband signal falls within the selectioncorridor, the threshold comparator 124 generates a trigger signalS_(TR). The trigger signal S_(TR) is provided to a memory element 128and a counter 126. The trigger signal S_(TR) causes the memory element128 to accumulate amplitude and phase sample of an associated RF signal,as measured by the measurement unit 118 on paths 120. Over a timeperiod, the memory element 128 collects a plurality of RF signal sampleswhich correspond to substantially constant baseband amplitude values(i.e., amplitude values within the selection corridor). The triggersignal S_(TR) also causes the counter 126 to increment its value totrack the number of accumulated RF signal samples in the memory element128.

When the time period is exceeded (e.g., when the number of measurementsexceeds a predetermined number), the counter 126 causes a tuningcalculator 122 to analyze the measured samples accumulated in the memoryelement 128. To reduce the measurement errors and increase the impedanceprecision, the tuning calculator 122 is configured to average theaccumulated amplitude and phase values. Sample accumulation is donetwice (e.g., during a first time period and a second time period) pertimeslot resulting in four average values (e.g., two amplitude and twophases). In one embodiment, samples are first accumulated for a forwardpropagating wave and then the memory unit 128 and counter 126 are resetto zero and the same procedure is repeated for a reflected wave. Basedon these averaged values, the tuning calculator 122 generates a controlsignal 116 that is provided to the RF antenna tuner 112, which changesits impedance in response to the control signal 116 to limit impedancemismatch between the RF antenna 114 and RF transmission path 104 for agiven use case. The control signal 116 may be updated from time to timeto reflect changes in use cases and/or frequency, thereby helping tokeep the antenna 114 “tuned” to the RF transmission path 104 on arelatively continuous basis.

FIG. 2 is a block diagram of a more particular embodiment of a disclosedtransmitter comprising a polar modulator. The transmitter 200 includes afirst CORDIC 202, which is configured to receive in-phase (I(t)) andquadrature phase (Q(t)) signal components. The first CORDIC 202 convertsthe I(t) and Q(t) signal components from a Cartesian format to a polarequivalent amplitude signal A_(BB) and phase signal φ_(BB), which aresent as baseband signals to the RF transmission path 204. The RFtransmission path 204 includes a modulator 212, comprising a localoscillator (LO) 218 and a polar modulator 220, which is configured toup-convert the amplitude and phase baseband signals A_(BB), φ_(BB) to anRF signal having amplitude and phase modulation, which is provided to apower amplifier 214 and then to an analog front end 216. Because theamplitude modulation is controlled by the amplitude baseband signal,selective sampling of the RF signal, based upon the amplitude basebandsignal A_(BB), enables more precise impedance calculations over a shorttime period.

A threshold comparator 240 is configured to receive the amplitudecomponent of the baseband signal (i.e., the amplitude signal A_(BB))output from the first CORDIC 202. A delay element 239 is configured tocompensate for the propagation delay in RF units (e.g., 214-216, and220-234) (i.e., without the delay element 239, the samples accumulatedby accumulation units 236 and 238 will not represent the basebandamplitude value detected in threshold comparator 240). The thresholdcomparator 240 determines if the amplitude of the baseband signal iswithin a selection corridor defined by an upper and a lower thresholdvalues. If the amplitude signal A_(BB) is within the selection corridor,the threshold comparator 240 generates a trigger signal S_(TR) that isprovided to a first accumulation unit 236 (e.g., for amplitude samples),a second accumulation unit 238 (e.g., for phase samples), and a counter242. The trigger signal S_(TR) causes the first and second accumulationunits to respectively accumulate measured RF signal amplitude and phasesamples associated with the baseband signal. The trigger signal S_(TR)also increments the counter 242, thereby tracking a number ofaccumulated samples stored in the first and second accumulation units.

As illustrated in FIG. 2, RF signal amplitude and phase samples aremeasured by way of a directional coupler 222 that is coupled to thefeedback receiver 206 via a switch 224. The switch 224, under thedirection of a control unit 246, provides forward propagating andreflected waves to the feedback receiver 206 from the directionalcoupler 222. The waves pass through first and second mixers, 228 a and228 b, and to a second CORDIC 230. In one embodiment, the second CORDIC230 is configured to calculate amplitude and phase samples every clockperiod, and when the baseband signal has an amplitude that falls withinthe selection corridor the amplitude and phase values are accumulated infirst and second accumulation units 236 and 238.

For example, during operation, when the control unit 246 enables a firstoutput 226 a of the directional coupler 222, the second CORDIC 230outputs amplitude and phase samples of forwarded signals to magnitudeand phase registers, 232 and 234, over a first time period. During eachclock period of the first time period, the amplitude of the basebandsignal is compared to a selection corridor. If the amplitude of thebaseband signal is within the selection corridor, the thresholdcomparator 240 generates a trigger signal S_(TR) that causes the firstand second accumulation units, 236 and 238, to accumulate acorresponding measured RF signal amplitude and phase sample. If theamplitude of the baseband signal is not within the selection corridor,the threshold comparator 240 does not send the trigger signal S_(TR) andthe corresponding RF signal amplitude and phase sample is notaccumulated. Such selective accumulation is performed for a plurality offorward wave samples over the first time period, allowing for aplurality of phase and amplitude samples to be stored for clock periodsin which an amplitude of the baseband signal is within the selectioncorridor (i.e., has a substantially constant value). At the end of thefirst time period (e.g., at the middle of a timeslot), the accumulatedforward wave amplitude and phase samples are averaged and read into acalculator 244.

The accumulation units, 236 and 238, are then reset and the control unit246 subsequently enables a second output 226 b of the directionalcoupler 222, allowing registers 232 and 234 to store reflected amplitudeand phase samples output by the second CORDIC 230 over a second timeperiod. During each clock period of a second time period, the amplitudeof the baseband signal is compared to the selection corridor. It will beappreciated that for baseband signals signal in first and second timeperiods, the selection corridor is selected to be the same so thatbaseband amplitude samples have constant values over both time periods.If the amplitude of the baseband is within the selection corridor, thethreshold comparator 240 generates a trigger signal S_(TR) that causesthe first and second accumulation units, 236 and 238, to accumulate acorresponding measured RF signal amplitude and phase sample. If theamplitude of the baseband signal is not within the selection corridor,the threshold comparator 240 does not send the trigger signal. Suchselective accumulation is performed for a plurality of reflected wavesamples over the second time period. At the end of the second timeperiod (e.g., at the end of a timeslot), the accumulated reflected waveamplitude and phase samples are averaged and read into the calculator244.

In one embodiment, the first and second time periods are defined as atime it takes for a number of amplitude and phase samples to reach apredetermined number “M” (e.g., M=128). When the predetermined number“M” is reached, the counter 242 will send a signal to the calculator 244indicating that a sufficient number of samples have been received. Inanother embodiment, the counter 242 is configured to send the number ofcollected samples after a given time period (e.g., 20 μs) has elapsed,so that the calculator 244 can perform a calculation of the impedance ofthe system based upon the collected number of samples.

When the calculator 244 (which is often implemented in software runningon a microprocessor) receives a signal from the counter 242, itgenerates a control signal, based on the average phase and amplitudevalues for the forward-propagating and reflected waves, which isprovided to the antenna tuner 208. The tuning signal adjusts theimpedance of the antenna tuner 208 to limit any impedance mismatchbetween the analog front end 216 and the antenna 210.

It will be appreciated that although FIG. 2 illustrates the accumulationunits as comprising separate logic elements, in various otherembodiments, the accumulation units may be comprised as part of anothercomponent of the feedback receiver. For example, in an embodiment, theaccumulation units, 236 and 238, may be realized inside the calculator244 as registers (illustrated as direct connections from registers 232and 234 to calculator 244).

FIG. 3 is a graph 300 showing an exemplary baseband signal havingamplitude modulation. In particular, FIG. 3 illustrates a comparison ofthe baseband signal amplitude to a selection corridor comprising twothreshold values (e.g., as done by threshold comparator 240 in FIG. 2).In particular, graph 300 illustrates the amplitude of the basebandsignal on the y-axis and time on the x-axis (measured in digital clockperiods).

As illustrated in graph 300, the baseband signal 302 is shown over atimeslot 306, which may be assigned to a transmitter via a base stationor other wireless communication device. Since a feedback receiver cannotbe switched quickly to measure forward propagated or reflected signals(e.g., since it includes filters and/or amplifiers having a slowresponse time), switching between measurements of forward propagated andreflected waves may be done once per timeslot (e.g., switched once inthe middle of the timeslot 306). For example, during a first time period308, a transmitter can set its directional coupler (e.g., correspondingto directional coupler 222 in FIG. 2) to propagate a forward wavethrough the transmitter's feedback receiver, while during a second timeperiod 310, the transmitter can set its directional coupler to propagatea reflected wave through the transmitter's feedback receiver.

During operation, a threshold comparator is configured to compare theamplitude of the baseband signal with a selection corridor 304 definedby a first, upper threshold value (TH_(up)) and a second, lowerthreshold value (TH_(low)). If the amplitude of the baseband signal 302is within the selection corridor 304, then a measurement of theamplitude and phase samples of an associated RF signal is accumulated(e.g., by accumulation units 236 and 238 in FIG. 2).

For example, at a first clock period t₁, the baseband signal 302 has anamplitude value that falls outside of the selection corridor 304,causing no forward propagated wave amplitude and phase samples to beaccumulated and a counter is not incremented. At a second clock periodt₂, the baseband signal 302 has an amplitude that falls within theselection corridor 304. Since the amplitude of the baseband signal fallswithin the selection corridor 304, a measured amplitude sample of aforward propagated RF signal is stored in a first accumulation unit, ameasured phase propagated of the forward propagated wave is stored in asecond accumulation unit, and a counter is incremented to a first value(e.g., 1). During a third clock period t₃, the baseband signal 302 againhas an amplitude that falls within the selection corridor 304, so thatmeasured amplitude and phase samples of a forward propagated RF signalare added to the first accumulation unit (already storing an amplitudesample) and the second accumulation unit (already storing a phasesample), and the counter is incremented to a second value (e.g., 2).When a sufficient number of “M” samples are accumulated (or apredetermined time has elapsed), the first time period 308 ends and thecalculator divides the accumulated phase and amplitude values by “M” (orN<M) to determine average values of amplitude and phase of theaccumulated forward propagated waves over the first time period 308.

At a later time t_(s) (e.g., in the middle of the timeslot 306)reflected waves are measured. The amplitude of the baseband signal 302is compared to a selection corridor 304 (e.g., the same corridor usedfor forwarded waves) and amplitude and phase samples of the reflected RFsignal propagating through the directional coupler are correspondinglymeasured and selectively accumulated (e.g., at clock period t_(n−4), abaseband signal has an amplitude sample that falls within of theselection corridor, causing amplitude and phase values to be accumulatedand the counter is incremented, while at clock period t_(n−3), abaseband signal has an amplitude value that falls outside of theselection corridor, causing amplitude and phase sample not to beaccumulated and the counter not to be incremented).

Based on averages of the forward propagated and reflected samplesaccumulated during the timeslot 306, at time 312 the transmittercalculates a change in impedance that will limit impedance mismatchbetween an RF transmission path and an RF antenna. Subsequently, at time314 the transmitter implements the change.

Accordingly, restricting measurements of the RF signal amplitude andphase to baseband signals having an amplitude falling within theselection corridor 304 can be seen as taking a measurement from a signalwithout amplitude modulation (e.g., which is an ideal measurement case)or as a result of long time filtering with narrow band LPF, where theamplitude modulation component is sufficiently removed.

It will be appreciated that the size of the selection corridor 304 maybe varied (e.g., by varying the upper and lower threshold values) toeffectuate transmitter operation in various embodiments. However, thereis a tradeoff between the size of selection corridor 304, measurementtime, and impedance accuracy. The bigger the selection corridor 304, thefaster measured samples will accumulate, but the larger the impedancemeasurement error. If the selection corridor is selected to be verynarrow (e.g., 1 unit), then a single measurement in first time periodand another one in the second period will be enough for an absoluteprecise impedance calculation. However, since no samples may fall intosuch a very narrow selection corridor, the selection corridor is oftenmade wider and an average of several measured samples is implemented. Inone embodiment, to reduce the measurement time and increase theprobability of baseband samples being inside the selection corridor 304,the upper and lower threshold values, TH_(up) and TH_(low), may beselected to be symmetrically around the RMS value of baseband signal 302(e.g., +/−2.5% around baseband RMS value).

FIG. 4 illustrates an alternative embodiment of a disclosed transmitter400 comprising a transmission path 402 having an IQ modulator 410. TheIQ modulator 410 includes a local oscillator 416, a 90° phase shiftmodule 418, first and second mixers 420 a and 420 b, and a summationelement 422. The first and second mixers 420 a and 420 b are configuredto receive baseband in-phase (I(t)) and quadrature phase (Q(t)) signalsand to convert the baseband I(t) and Q(t) signals to RF frequencysignals, which are combined by the summation element and then providedas an IQ modulated RF stream to a power amplifier 412 and an analogfront end 414.

A directional coupler 424 is coupled to the feedback receiver 404 by wayof a switch 426 controlled by a control unit 450. The control unit 450operates the feedback receiver 404 to selectively accumulate a pluralityof RF signal amplitude and phase samples, corresponding to a basebandsignal having a substantially constant amplitude, before calculating acontrol signal. When the control unit 450 passes a first output of thedirectional coupler 424 to the FBR, the forward propagating wave fromthe directional coupler 424 passes through first mixer and second mixers428 a and 428 b and then a first pair of mixers 430 a and a second pairof mixers 430 b. One of the mixers of each of the first and second pairsof mixers are coupled to a first summation element 432 a, and the otherof the mixers of each of the first and second pairs of mixers arecoupled to a second summation element 432 b. The first and secondsummation elements are coupled to an amplitude and phase register 434and 436.

An amplitude calculator 442 is configured to determine an amplitude ofthe I(t) and Q(t) baseband signals. The amplitude calculator 442 isconnected to the baseband I(t) and Q(t) baseband signals via delayelements 441 a and 441 b. The delay elements, 441 a and 441 b, areconfigured to compensate for the propagation delay in RF units (e.g.,412-414 and 420-438). The amplitude is then provided to a thresholdcomparator 444, which determines if the amplitude of the baseband signalis within a selection corridor. When the amplitude is within theselection corridor, the threshold comparator 444 outputs a triggersignal at an output node to the first and second accumulation units 438and 440, which are coupled to the output node. The trigger signal causesthe first and second accumulation units 438 and 440 to receive theamplitude and phase values stored in the registers.

The first accumulation unit 438 contains a summation element 438 a and aflip-flop 438 b. The summation element 438 a is configured to receive anamplitude sample at each clock period and to selectively add it to afeedback signal output from flip-flop 438 b. In particular, theflip-flop 438 b has a first input configured to receive an output of thesummation element 438 a, a clock input configured to receive a triggersignal output from the threshold comparator 444, and a reset inputoutput from the control unit 450. When the trigger signal received atthe clock input changes (e.g., goes from low to high), the output of theflip-flop is set equal to the first input signal. If the trigger signalreceived at the clock input doesn't change (e.g., remains low), theoutput of the flip-flop remains the same as in a previous clock period.Therefore, the trigger signal received at the clock input allows theaccumulation unit 438 to accumulate a plurality of amplitude samplesover a time period. If the “reset” signal is received at the resetinput, the value accumulated in the flip-flop is reset (e.g., when atime period is over). The second accumulation unit 440 operates insubstantially the same manner to accumulate phase samples over a timeperiod.

In one embodiment, after collecting a number of samples the counter 446is configured to generate a “stop” signal. The stop signal is providedto the calculator 448, which reads the accumulated amplitude and phasesamples for the time period. The calculator 448 is configured tocalculate an average values of amplitude and phase samples for forwardpropagated and reflected waves. In another embodiment, if the number ofcollected samples doesn't reach the predetermined number “M” within apredetermined time, then the counter 446 sends a “stop” signal and anumber of accumulated samples “N” to the calculator 448. In oneembodiment, the calculator 448 utilizes the “N” samples to calculate theaverage values. In another embodiment, the calculator 448 mayextrapolate the received “N” samples to reach the predetermined numberof samples “M” (e.g., repeat last stored amplitude and phase samples toreach the “M” number).

The control unit 450 subsequently changes the switch 426 so a secondoutput of the directional coupler 424 is passed to the feedback receiver404, and a reflected wave propagates through the mixers and summationelements, until being stored in accumulation elements. When the controlunit 450 changes the switch 426 it generates a “start” signal whichrestarts the counter from 0 and which resets the accumulation units 438and 440.

At the end of a timeslot the calculator 448 has average values for theforwarded and reflected amplitude and phases (e.g., Mag_for, Phase_for,Mag_ref, Phase_ref). From these average values, the calculator cancalculate a complex admittance at the antenna tuner input according tothe expressions (e.g., for a 50 ohm target impedance):Y _(—) re _(—) tun=1/50*(1+Mag _(—) rel*COS(Del _(—) Ph))Y _(—) im _(—) tun=1/50*Mag _(—) rel*SIN(Del _(—) Ph),where Mag_rel=Mag_ref/Mag_for=a relation between two magnitudes, andDel_Ph=Phase_ref−Phase_for=difference between two phases. Because thecurrent antenna admittance and the tuner's internal structure is known,the transmitter can calculate the new values for the tuner's elements tomatch the current antenna admittance to the wanted impedance (e.g., 50Ohm). It will be appreciated that in the IQ modulation scheme of FIG. 4,the values of Mag_rel*COS(Del_Ph) and Mag_rel*SIN(Del_Ph) for PMtransmitter are calculated automatically because of the workingprinciple of FBR using a modulated local oscillator

Based on the calculated admittance values, the calculator 448 (which isoften implemented in software running on a microprocessor) generates acontrol signal that adjusts the impedance of the antenna tuner 406 tolimit any impedance mismatch between the analog front end 414 and theantenna 408 for the timeslot and/or for subsequent timeslots.

FIG. 5 shows a graph 500 of impedance measurements taken by a feedbackreceiver calculator (e.g., corresponding to calculator 448 in FIG. 4).In FIG. 5 the imaginary component of the impedance is shown on they-axis and the real component of the impedance is shown on the x-axis.

Impedance measurements 502 are calculated from averages taken by afeedback receiver that does not utilize a threshold calculator. Asillustrated in graph 500, the samples have a relatively large impedancespread that causes inaccuracies in impedance matching.

Impedance measurements 504 are calculated from averages taken by afeedback receiver that does utilize a threshold calculator (e.g.,corresponding to threshold calculator in FIG. 4). In particular, theimpedance measurements 504 were obtained using a selection corridor thatis +/−2.5% around the baseband signal RMS value. The number of measuredsamples (M) is set to 128 and the predetermined time is limited to 20us. By limiting the collection of RF amplitude and phase samples toassociated baseband signals having an amplitude falling within theselection corridor, substantially equal average amplitudes and phasesare achieved. The substantially equal averages provide for substantiallyequal impedance measurements. As illustrated in graph 500, impedancemeasurements 504 generated by a disclosed transmitter utilizing athreshold calculator have a low spread compared to impedancemeasurements 502 taken by a transmitter not utilizing a thresholdcalculator.

FIG. 6 illustrates flow diagram of an exemplary method 600 for adjustingan antenna tuning in accordance with some embodiments. While this method600 is illustrated and described below as a series of acts or events,the present disclosure is not limited by the illustrated ordering ofsuch acts or events. The same is true for other methods disclosedherein. For example, some acts may occur in different orders and/orconcurrently with other acts or events apart from those illustratedand/or described herein. In addition, not all illustrated acts arerequired, and one or more of the acts depicted herein may be carried outin one or more separate acts or phases.

The method 600 starts at 602, wherein a baseband signal is generated andan RF signal is generated from the baseband signal. In one embodiment,the baseband signal may comprise a polar signal having phase andamplitude components. In another embodiment, the baseband signal maycomprise in-phase and quadrature phase components offset by 90°. Thebaseband signal is converted to a radio frequency (RF) signal that issubsequently transmitted via an antenna.

At 604 a forward propagating wave is selected. In one embodiment, aforward propagating wave is selected by enabling a first output of adirectional coupler (e.g., directional coupler 108 in FIG. 1).

At 606 an amplitude and phase sample of an RF signal is measured. Theamplitude and phase sample is taken during a clock period of a firsttime period.

At 608 an amplitude of a baseband signal associated with the amplitudeand phase sample is compared to a selection corridor defined by upperand lower threshold values. The comparison ensures that the RF signalhas an approximately constant amplitude.

At 610, if the amplitude of the baseband signal is not within theselection corridor, a measurement of an RF amplitude and phase isperformed for a next clock period (at 604) of the time period and acomparison of an associated baseband signal is repeated (at 608). If theamplitude of the baseband signal is within the selection corridor, themeasured amplitude and phase sample is accumulated at 612.

At 614 a counter value is incremented. Incrementation of the countervalue keeps track of the number of accumulated amplitude and phasesamples for a forwarded or reflected wave.

At 616, if the counter number (N_(C)) is greater than a predeterminednumber (N_(PRE)) accumulation of amplitude and phase samples is stoppedat 620. If the counter number (N_(C)) is not greater than apredetermined number (NPRE), but a predetermined time is exceededaccumulation of the amplitude and phase samples is stopped at 620. Ifthe counter number is not greater than the predetermined number and apredetermined time has not elapsed, the method returns to 606 andanother amplitude and phase sample is measured in a next clock period ofthe time period.

At 622 average values of the accumulated amplitude and phase samples arecalculated. In one embodiment, when a sufficient number of “M”measurements/samples have been taken, the average values of amplitudeand phase samples accumulated over a time period is determined bydividing the accumulated phase and amplitude values by “M”. In oneembodiment, when a number of measurements “N”<“M” have been taken, but apredetermined time has elapsed, the average values of amplitude andphase samples accumulated over the predetermined time is determined bydividing the accumulated amplitude and phase samples by “N”.

At 624, a reflected propagating wave is selected. In one embodiment, thereflected propagating wave is selected by enabling a second output of adirectional coupler. Steps 606 to 622 are repeated for the reflectedwave to determine an average value of an amplitude and phase of thereflected wave for a second time period (e.g., one half of a timeslot).

At 626, based on the average values of the accumulated amplitude andphase samples for forward propagating and reflected waves, an admittanceis calculated. In one embodiment, a tuner input admittance can becalculated from the averages values and based on the tuner inputadmittance and the tuner's known structure (see e.g., FIG. 2), anadmittance at the tuner output, which is equal to the admittance at RFantenna input is calculated.

At 628, the method adjusts an antenna tuner so the impedance of the RFtransmission path matches the impedance of the RF antenna. In manyembodiments, the impedance adjustment is made at a symbol boundarybetween two time slots to prevent the adjustment from corrupting thetransmitted signal. In this way, a present antenna tuner setting isassumed to be valid until the transmission frequency is changed or untilimpedance mismatching exceeds a predetermined threshold. To checkmatching, measurements can be repeated from time to time even if thetransmission frequency is constant. In some embodiments, calculationsand antenna tuner updating can be performed only when a change intransmission frequency occurs or when high amounts of impedance mismatchoccur.

Although the disclosure has been shown and described with respect to oneor more implementations, equivalent alterations and modifications willoccur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Forexample, it will be appreciated that identifiers such as “first” and“second” do not imply any type of ordering or placement with respect toother elements; but rather “first” and “second” and other similaridentifiers are just generic identifiers. In addition, it will beappreciated that the term “coupled” includes direct and indirectcoupling. The disclosure includes all such modifications and alterationsand is limited only by the scope of the following claims. In particularregard to the various functions performed by the above describedcomponents (e.g., elements and/or resources), the terms used to describesuch components are intended to correspond, unless otherwise indicated,to any component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature of the disclosuremay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. In addition, the articles “a”and “an” as used in this application and the appended claims are to beconstrued to mean “one or more”.

Furthermore, to the extent that the terms “includes”, “having”, “has”,“with”, or variants thereof are used in either the detailed descriptionor the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising.”

What is claimed is:
 1. A transmitter, comprising: analysis circuitryconfigured to receive at least an amplitude portion of a baseband signaland a radio frequency (RF) signal based on the baseband signal, whereinthe analysis circuitry is selectively operated based upon the amplitudeportion of the baseband signal to obtain samples of the RF signal, todetermine an impedance mismatch between a transmission path and an RFantenna from the obtained samples, and to generate a control signalbased on the determined impedance mismatch; and an RF antenna tunercoupled to the analysis circuitry and configured to couple to the RFantenna via an RF antenna port, wherein the RF antenna tuner is tuned toreduce the determined impedance mismatch according to the control signalgenerated by the analysis circuitry.
 2. The transmitter of claim 1,wherein the analysis circuitry comprises: a threshold comparator coupledbetween a baseband signal generator and the transmission path, whereinthe threshold comparator is configured to output a trigger signal at anoutput node if the amplitude of the baseband signal is within aselection corridor defined by upper and lower threshold values; and amemory element coupled to the output node and configured to storeobtained amplitude and phase samples of the RF signal during clockperiods in which the trigger signal is generated.
 3. The transmitter ofclaim 2, wherein the analysis circuitry further comprises: a counterconfigured to count a number of the obtained amplitude and phase samplesduring a time period comprising a plurality of clock periods.
 4. Thetransmitter of claim 2, wherein the analysis circuitry comprises: adirectional coupler coupled between the transmission path and theantenna tuner; and a measurement unit configured to measure a pluralityof amplitude and phase samples of a forward propagating wave provided bythe directional coupler during a first time period, and furtherconfigured to measure a plurality of amplitude and phase samples of areflected wave provided by the directional coupler during a second timeperiod.
 5. The transmitter of claim 4, wherein the memory elementcomprises: a first storage unit coupled to the output node andconfigured to store the measured amplitude samples for the forwardpropagating wave during clock periods in which the trigger signal isgenerated during the first time period and further configured to storethe measured amplitude samples for the reflected wave during clockperiods in which the trigger signal is generated during the second timeperiod; and a second storage unit coupled to the output node andconfigured to store the measured phase samples for the forwardpropagating wave during clock periods in which the trigger signal isgenerated during the first time period and further configured to storethe measured phase samples for the reflected wave during clock periodsin which the trigger signal is generated during the second time period.6. The transmitter of claim 5, wherein the analysis circuitry furthercomprises: a calculator configured to generate the control signal basedon average values of the obtained amplitude and phase samples of theforward propagating wave and average values of the obtained amplitudeand phase samples of the reflected wave.
 7. The transmitter of claim 6,wherein the calculator determines the average values of the amplitudeand phase samples of the forward propagating wave and of the reflectedwave after a number of the obtained amplitude and phase samples exceedsa predetermined number.
 8. The transmitter of claim 6, wherein thecalculator determines the average values of amplitude and phase samplesof the forward propagating wave and of the reflected wave after apredetermined time has elapsed.
 9. The transmitter of claim 6, whereinthe analysis circuitry further comprises: a control unit coupled to thedirectional coupler and configured to set the directional coupler to afirst state to measure the plurality of amplitude and phase samples ofthe forward propagating wave, and further configured to set thedirectional coupler to a second state to measure the plurality ofamplitude and phase samples of the reflected wave; first and secondmixers having respective first inputs coupled to an output of thedirectional coupler and having respective second inputs to receive alocal oscillator (LO) signal; and a CORDIC coupled to the first andsecond mixers and configured to output amplitude and phase samples basedon the output of the directional coupler.
 10. The transmitter of claim1, wherein the transmission path comprises: an IQ modulator having aninput and output; a power amplifier having an input and output, whereinthe input of the power amplifier is coupled to the output of themodulator; and an analog front end having an input and an output,wherein the input of the analog front end is coupled to the output ofthe power amplifier and wherein the output of the analog front end iscoupled to the RF antenna tuner.
 11. The transmitter of claim 1, whereinthe transmission path comprises: a polar modulator having an input andoutput; a power amplifier having an input and output, wherein the inputof the power amplifier is coupled to the output of the modulator; and ananalog front end having an input and an output, wherein the input of theanalog front end is coupled to the output of the power amplifier andwherein the output of the analog front end is coupled to the RF antennatuner.
 12. A method, comprising: comparing an amplitude of a basebandsignal to a selection corridor, wherein if the amplitude is within theselection corridor a corresponding amplitude and phase sample of an RFsignal that is related to the baseband signal is stored in a memoryelement; calculating and storing average values of the amplitude andphase samples obtained over a time period; and adjusting an admittanceof an antenna tuner to set a matching condition between the antennatuner and an RF antenna port configured to couple to an RF antenna basedon the average values of the amplitude and phase samples.
 13. The methodof claim 12, wherein a plurality of amplitude and phase samples areobtained for a forward propagating wave during a first time period; andwherein a plurality of amplitude and phase samples are obtained for areflected wave during a second time period, immediately after the firsttime period.
 14. The method of claim 13, wherein the first time periodand the second time period are both included in a timeslot assigned by abase station.
 15. The method of claim 12, wherein calculating andstoring average values comprises: counting a number of obtainedamplitude and phase samples over the time period; and dividing theobtained amplitude or phase samples by the number of obtained amplitudeand phase samples.
 16. The method of claim 15, wherein calculating theaverage values of the amplitude and phase samples is performed after thenumber of obtained amplitude and phase samples exceeds a predeterminednumber.
 17. The method of claim 15, wherein calculating the averagevalues of the amplitude and phase samples is performed after apredetermined time has been exceeded.
 18. A transmitter, comprising: anantenna tuner; a threshold comparator configured to generate a triggersignal at an output node if an amplitude of a baseband signal is withina selection corridor defined by upper and lower threshold values; amemory element configured to store obtained amplitude and phase samplesof an RF signal that is based on the baseband signal during clockperiods in which the trigger signal is generated; a counter configuredto count a number of obtained amplitude and phase samples during a timeperiod comprising a plurality of clock periods; and a calculatorconfigured to provide a control signal to tune the antenna tuner,wherein the control signal is based on average values of the obtainedamplitude and phase samples of a forward propagating wave and averagevalues of the obtained amplitude and phase samples of a reflected wave.19. The transmitter of claim 18, wherein the calculator determines theaverage values of the amplitude and phase samples of the forwardpropagating wave and of the reflected wave after a number of theobtained amplitude and phase samples exceeds a predetermined number. 20.The transmitter of claim 18, wherein the calculator determines theaverage values of amplitude and phase samples of the forward propagatingwave and of the reflected wave after a predetermined time has elapsed.